1. Field of the Invention
The present invention relates to an optical gauging apparatus utilizing the light reflected on an object to be gauged and being useful for car level gauging, spring deflection gauging, photographic distance gauging, etc.
2. Background Art
There have already been proposed various gauging apparatuses utilizing the reflected light on an object to be gauged, an example of which is schematically shown by FIG. 24 of the accompanying drawings.
This example of prior art is a distance gauging apparatus for photographic camera and based on the principle of triangulation as illustrated. With this gauging apparatus, the light emitted from a light source 1 comprising a light emitting diode is condensed by a light projecting lens 2 and then projected onto an object 3 to be photographed.
The light reflected on the object 3 is condensed by a light receiving lens 4 and then focussed on a predetermined location of a light receiving element 5 such as PSD (Poositon Sensing Device) or CCD. Consequently, a light receiving angle .theta..sub.1 depends on a position of the object 3 and a distance Do to the object 3 is determined from said light receiving angle .theta..sub.1, in relation to preselected light projecting angle .theta..sub.2 and inter-lens distance l.
In the case of the above-mentioned gauging apparatus shown by FIG. 24, a light spot focussed on the light receiving element 5 is preferably as small as possible and, to achieve this, high optical properties are required for respective parts such as the light source 1, the light projecting lens 2 and the light receiving lens 4.
In the case of a short-distance gauging, the light receiving angle .theta..sub.1 is necessarily reduced but here again it is essential to focus a light image of the object 3 as sharply as possible on the light receiving element 5. To meet such requirement, a wide angle lens having a large image circle must be employed as the light receiving lens 4. This leads to an increased cost and requires high mechanical precision for the light receiving angle .theta..sub.1, the light projecting angle .theta..sub.2, the inter-lens distance l, etc.
A distance from the light source 1 to the light projecting lens 2 must be adjusted for sharply focussing the light image of the light source 1 on the object 3 and similarly a distance from the light receiving lens 4 to the light receiving element 5 must be also adjusted for sharply focussing the light image of the object 3 on the light receiving element 5. A mechanism for such adjustment is inevitably complicated.
Another example of prior art illustrated by FIG. 25 is a gauging apparatus generally incorporated, as one of active features, into the auto-focussing mechanism for photographic camera. In this apparatus, an object 8 to be photographed is illuminated by the light projected from a light source 6 such as a light emitting diode. The light reflected on the object 8 is received by a light receiving element 7 such as a photodiode. A light receiving level of the light receiving element 7 (i.e., intensity of the reflected light) is detected and a distance Do to the object 8 is determined from the detected value.
The gauging apparatus of FIG. 25 is often disadvantageously affected by a particular environment in which the projected light is reflected on the object 8.
Specifically, an object 8 having a dark surface presents the light receiving level different from that which an object 8 having a bright surface presents, because these objects 8 having different surfaces have correspondingly different reflection factors. Also when the light source 6 has its light emitting surface contaminated or the light receiving element 7 has its light receiving surface contaminated, the intensity of the emitted light or the light receiving level respectively varies.
Thus the light receiving sensitivity is affected by various conditions such as uniform reflection factor and contaminated surface of the object 8, or contaminated surface of the light source 6 or the light receiving element 7, making it difficult to gauge an accurate distance.